Controlling system



vMm!21,1944- L. B. HADDAD 2,344,608 I CONTROLLING SYSTEM Filed Sept. 19, 1940 5Shefs-Sheet 1 INVENTOR I March 21, 1944.

1,. B. HADDAD CONTROLLING SYSTEM Filed Sept. 19,1940

Sheets-Sheet 2 Es.

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I I v \I o IO 2o so 40 9' Frequency O'yclu v INVENTOR La bee ,B. fiaddacl 0.6. Amps. (Aux. Excitufion) March 21, 1944.

File 1 Sept. 19. 1940 5 Sheets-Sheet 4' Operating range W 4 Alternator Field Excitafiqn, 38 Va":

Temp. of Auxiliary Field Winding, 20 C.

0 IO I 20 30 4o .50 so INVENTOR Y 2n) /l ywa vf ATTORNEYS March 21, 1944. B, AD 2,344,608

CONTROLLING SYSTEM File d Sept. 19, 1940 5 Sheets-Sheet; 5 W. 11. fi m a 1E. I At 625}:

E I59 Volts |,=.60OAmp.(Eq. Sme Wave) MSSAmMEnSiM E =I25 Volts E, 191.5 Volts 5-30 vom I =.O89Amp.(Eq.Sine Wave) EA =|25.2 vain.

INVENTOR Labeeb ,B. Hada aol Patented Mar. 21. 1944 2,344,608 CONTROLLING srs'rmu Labeeb B. Haddad. New Haven,

to The Safety Car Heating Conn., assignor and Lighting Company, 1nc., a corporation of Delaware Application September 19, 1940, Serial No. 357,430 Claims. (01. 111-419) This invention relates to control, and more particularly to the control of the speed or a motor alternator which receives power from a direct current source and delivers alternating current to fluorescent lights on railway cars.

An object of this invention is to provide a reliable and dependable source of alternating current of constant frequency and voltage. A further object is to provide a motor alternator which is capable of delivering alternating current having a minimum range of variation of frequency and voltage when the voltage of the direct current source of power varies over a wide range. A further object is to provide apparatus of the above character which is light in weight and emcient in operation and which is thoroughly practical in use. A still further object is to provide a. control for the effective magnetic field of the motor of a motor alternator. A further object is to provide a source of current on a motor-alternator set which current may be used to automatically regulate the driving speed depending upon the output frequency of the alternator. A further object'is to provide amethod of control and control means for a motor alternator of the above character which will receive alternating current from the alternator and deliver current which tends to maintain constant speed. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly consists in'the features of construction, combinations of elements, arrangements of parts and in the several steps and relation and order of each of the same to one or more of the others, all as will be illustratively described herein, and. the scope of the lowing claims.

In the drawings:

Figure 1 is a schematic showing of one em bodiment of the invention;

Figure 2 is a diagrammatic representation of t a portion of the apparatus shown in Figure 1;

Figure 3 is a simplified equivalent alternating current circuit of the speed regulating circuit. of Figures 1 and 2;

Figure 4 is a set of curves showing the variation with frequency of the direct current output of the control unit shown in Figures 1 and 2,

application of which will be indicated in the folv 'present invention, it

the voltage and current relationships in the embodiment of Figure 5 at alternator frequencies of 62 and 58 cycles per second respectively.

Figure 8 is a view similar to the right-hand portion 'of Figure 1, but showing another embodiment of the invention;

Figure 9 corresponds to Figure 2 and relates to the circuit of Figure 8.

Figure 10 "is similar output frequency varies in the embodiment of Figure 8;

Figure 11 is similar to Figure 5, but shows the currents and voltages of Figures 12 and l3;

Figures 12 and 13 are vector diagrams showing the voltage and current relationships in the circuit of Figure 8 at the alternator frequencies of 62 and 58 cycles per second, respectively; and Figure 14 is a view similar to Figures 2 and 9, but showing another embodiment of the invention.

This application is a continuation-in-part of my copending application I Serial Number 186,306, filed January 22, 1938,

entitled Voltage control,

which has issued as Patent No. 2,236,173, dated March 2?, 1941.

As conducive to a clearer understanding of the should be noted that the present embodiments are particularly suited for use on railway cars in providing a source of power for fluorescent lights. It is therefore important that the equipment be light in weight and sturdy in construction and that it be adaptable for use under varying conditions. On railway cars such as coaches, pullman cars and the like each car is provided with its own individual electrical system. This system generally includes a set of storage batteries, lighting and other equipment, and an axle-driven direct current generator to supply power for he equipment and for charging the batteries. In the present invention, direct current power is taken from the system to drive a motor and this motor in turn: drives an alternator which supplies alternating current to fluorescent lights. Railway equipment should be dependable in action and it should not require constant adjustment or repairing as it is diflicult to insure that the equipment will receive proper attention during use. p

The voltage. in the usual direct current electrical system varies during operation between 28 volts and 45 volts depending upon the condition of charge or the batteries. andupon whether or not current is being supplied by the direct current generator. Furthermore, the voltage may I p to Figure 4, and shows the variation in direct current output as-the vary when there are changes in the load, and thus with the present system, a change in the lighting load may tend to cause a change in the speed the motor alternator. It is an object oi this invention to provide apparatus of the above character which will constitute a reliable source of alternating current under the above conditions.

Referring particularly to the left-hand side of Figure 1 of the drawings, a generator 2 is provided with a controller 4 which maintains the proper current in the generator field 6. One side of the generator is connected through a line 1 and a switch in to a line H and a set of batteries 12; this line H is connected through a manual switch 8 to a line 8. The other side of the generator is connected through a line H to the other side of the batteries. Lines II and H are the main power lines of the battcry generator system which carries a load 15 consuming direct current. When switch 9 is closed, the voltage across lines 8 and I4 is the same asthat of lines II and I4, and this voltage varies depending upon the state of charge of the set of batteries and the starting and stopping of the chargingaction of the generator. Connected across lines 8 and II, and thus adapted to be energized by the voltage of the battery-generator system, is a direct current motor l8 having a main shunt field winding l1, a starting winding IQ for producing high starting torque and an armature 20. Armature is connected through a shaft 22 to drive the armature 24 01' an alternator indicated at 26 and having a main field winding and an auxiliary field winding 21. The alternator output brushes are connected to a pair of alterhating current lines 28 'and 30 which supply alternating current to a load 32 embodiment, is a bank or fluorescent lights and their attendant auxiliaries.

The main alternator field winding 25 has one side connected directly to line i l-and the other side connected through a resistor 38 to line 8. The alternator auxiliary field winding 21 is connected in series with the motor armature 20 and the starting winding 19, so that both 0! the windings l9 and 21 carry the motor armature current. Accordingly, winding I 9 is effective during the starting period to supply the proper field flux, and winding 21 is effective during the running period to exert control upon the alternator voltage. When there is a load on the alternator, any increase in the load causes an increase in motor armature current which flows through winding 21 and causes a corresponding increase in the alternator field excitation. In this way, winding 21 compensates the alternator for armature-reaction, and the alternator voltage tends to remain constant with changes in the load.

The main motor field winding l1 has one side connected through a resistance unit 42 to line 8. and the other side connected to the juncture of armature 20 and winding 21 and thus through winding 21 to line H. Winding 21 is a low resistance current winding and has a very small voltage drop across it, and therefore, the voltage across winding I1 and resistance unit 42 is substantially the same as the voltage across lines 8 and l4. Resistance unit 42 is made as large as possible in proportion to the resistance of winding l1 and the resistance unit has a substantially zero temperature-resistance coeflicient. Thus, variations in the resistance of winding i1 due to temperature changes have a minimum effect.

As indicated above, the magnetic field r alter.

which, in this i nator 26 is produced by the main alternator field winding 25 and the auxiliary alternator field winding 21. Main field winding 25 is connected across lines 8 and M in series with a resistance unit 36 which has a substantially zero temperature-resistance coeificient, and which reduces the eiTect of changes in resistance of winding 25 in the manner that resistance unit 42 reduces the effect of such changes in the motor field winding I1. The iron core of alternator 26 is such that the flux produced by alternator field winding 25 is substantially constant even though the voltage between lines 8 and l4 varies. Thus, the fiux produced by main field winding 25 tends to produce a constant voltage across the output lines and 30.

As indicated above, it is important that the motor alternator be maintained at substantially constant speed, even though there are changes in the applied voltage, the motor temperature, and the load. In the illustrative embodiments of the present invention, the motor field is varied to control the speed with the result that when the motor starts to slow down, the motor field clecreases; and when the motor starts to speed up, the motor field increases. This regulation of the field is dependent upon changes in the frequency of the alternator output voltage and, for all practical purposes, is independent of load and within the operating frequency range is much more sensitive to frequency variations than to voltage variations.

In carrying out this system of speed control, motor 18 is provided with an auxiliary speed-regulating field winding 2| which derives its current from the alternator output lines 28 and 30 through a resonant control circuit. In the illustrative embodiments, the resonant control circuit is formed by two reactors, two condensers and a rectifier; one of the reactors and one of the condensers are connected in a parallel resonant circuit, referred to as circuit A, and the other reactor and the other condenser are connected in another resonant circuit, referred to as circuit B. The rectifier unit has its output leads connected to the auxiliary field winding 2| of motor I8 and its input leads connected into circult B. Thus, from an electrical standpoint the parallel resonance circuit B includes the rectifier unit and theauxiliary field winding 2|.

Referring particularly to the right-hand side 30 of Figure 1, a double-sided iron core assembly 64 has a right-hand leg 63 upon which is inductance coil 62 which is the reactor of circuit B. Core assembly 64 has a left-hand leg 65 upon which is inductance coil 68 which is the reactor of circuit A. Circuit B also includes condenser 10 which is connected in parallel with inductance coil 62 at terminals 61 and 69. Circuit A includes a similar condenser 12' which is connected in parallel with inductance coil 68 at terminals 1| and 13. Inductance coil 68 is provided with a tap 14 which is connected through a lead 16 to line 28 of alternator 26, and terminal 69 is connected through a lead 82 to line 30 of alternator 2B. Inductance coil 62 is provided with a tap which is connected through a lead 18 to terminal 13. Rectifier unit 56 has one of its input terminals 53 connected through lead 59 to terminal 69, and its other input terminal 51 connected through a lead 58 to a tap 60 on inductance coil 62, The output terminals 55 and 5| of rectifier unit 56 are connected,- respectively, through leads 52 and 5 to the auxiliary field winding 2] of motor I8.

In this embodiment, condensers 10 and 12 are respectively.

tion purposes.

a,s44,ooa i 3 each of fifteen microfarads capacity and inductance coils 62 and 58 are of, .8 and .412 henries,

The number of turns between terminal 1| and tap 14 would be 29.3 per cent of the total number of turns of inductance coil 68 if there were no flux leakage between the turns. In order to compensate for the effect of leakage reactance resulting from leakage flux, the number of turnsbetween terminal 1| and tap II is less than the above-mentioned value. Similarly, the number of turns between terminal 61 and tap 80 would be 13.4 per cent of the total number of turns of the conductance coil 62, but is sufficiently less than 13.4 per cent to compensate for the effect of the leakage flux. The number of turns between tap 60 and terminal 69 is 34 per cent of the total number of turns of inductance coil 62. Core assembly H is provided with air gaps, there-being one gap at the center of each of legs 63 and 65 and there being a gap at the top of each of these legs, and the core assembly is so constructed that the iron of the core is, not saturated during normal operation. Alternator 26 normally operates at approximately sixty cycles per second and circuit A is so proportioned and constructed that it is in resonance at sixty-four cycles per second, while circuit B is in resonance at forty-six cycles per second. By providing an unsaturated core for each of the reactances, the resonance curves for circuits A and B are far more sensitive to changes in frequency than to changes in voltage. The output of the rectifier varies very rapidly with changes in frequency and comparatively slowly with changes in voltage.

The circuit resulting from connecting these various .units in the manner of Figure 1 is shown in Figure 2, there being a series circuit extending between thealternator output lines 28 and 3a which series circuit is formed by two parallel induetance-capacitance circuits-A and B. Induct ance-eapacitance circuit A is formed by condenser l2 and inductance coil 68, and circuit B is formed by condenser Ill, inductance coil 52 and the circuit of rectifier unit 56. It should be noted in considering the operation of the apparatus that the circuit may be considered as shown in Figure 3, which is a simplified equivalent circuit. Due to the use of taps on the inductance cells 68 and 62, the operation is the same as if condenser 12 were of thirty microfarads capacity and condenser were of twenty microfarads capacity. In Figure 3, the copper and iron losses of circuit A are represented by the central leg RA, and those of circuit B are represented by RB. In circuit B, the leg Rs includes the equivalent resistances of rectifier unit 56 and the speed-regulating field coil 2i as well as the equivalent resistances of the losses of condenser I0 and inductance coil '52.

During operation, the output voltage of the alternator which is impressed across the speedregulating circuit is distributed within the circuit depending upon the relative reactances. Referring to Figure 5, the total impressed voltage is represented by EL, while the line current is represented by In. The voltages across circuits A and B are represented by EA and En, respectively, and the current through the rectifier unit is represented by the notation Ia. As the speed of the alternator changes, the voltage and current relationships within the circuit change so that a different voltage is effective on theinput leads of the rectifier unit and there is a change in the value of current In. The circuits are so constructed and proportioned that the maximum current fiows in the speed-regulating field coil 2| at a frequency slightly below the minimum operation speed, and as the speed increases, the

. The embodiment of Figure 5 differs from that of Figures 1 and 2 in omitting taps 14 and onthe inductance coils, and the inductance. coils and the condeners are different in sizes. Accordingly in Figure 5, condensers 10' and 12' are of ZOniicrofarads and 30 microfarads capacity respectively, and inductance coils 62 and 68' are of .6 henry and .206 henry, respectively. In this embodiment, results are obtained similar to the results or the embodiment of Figures 1 and 2, and

because of its greater simplicity the circuit of Figure 5 is used wherever possible for illustra- Aocordingly the voltage and current designations of Figure 5 are represented by vector diagrams in Figures 6 and 7, though similar representations may be provided for the other embodiment.

value of this current drops off rapidly. As the speed and frequency increase toward and slightly beyond the maximum operating speed, the reduction in the current In continues to decrease at a rapid rate and reaches a value near zero. As indicated above, the speed-regulating field coil 21 is wound so that it tends to set up a fiux 0pposing the main field flux of the motor, and when In is at a high value, the effect of this current in coil 2| is sufficient to materially reduce the effective field flux of the motor. A decrease in the effective field fiux of the motor causes an increase in speed, and an increase in effectivefield flux causes a decrease in motor speed. At substantially the maximum motor speed, the effect'of current in field winding 2! is negligible and the motor speed depends upon the main field fiux produced by the shunt field winding i1. When the alternator s'peedstarts to decrease, the current In increases at a rapid rate with the result that the field coil 2| becomes effective to neutralize some of the effect of the main field winding. The immediate effect is a. reduction in the effective field fiux which tends to increase the motor speed. The net result is to minimise the change in speed.

In practice, variations in the speed of the motor alternator are caused by changes in the volt age driving the motor, changes in the motor temperature, which result in variations in field resistance and field current, and changes in load. For example, at 28 volts a standard shunt motor may have a speed of 3200 R. P. M., and at 45 volts the same motor may have a speed of'4000 R. P. M. Changes in motor temperature may result in an increase of twenty per cent in the resistance of the shunt field coil when the temperature of the field coil is raised from a cold condition to a hot" condition, and this results in an increase in motor speed of approximately eight per cent.

An increase in load on a shunt motor or a cumulatively compounded motor causes a decrease in speed. In the present embodiment, a curnuia tively compounded motor is shown, and accord ingly the total field flux of the motor is the .2 "n total of the effect of the shunt field winding plus the effect of the series field winding and minus the effect of the speed-regulating field coil. Omitting the effect of the speed-regulating field coil, the maximum speed would be reached when the temperature of the field winding is at a iim= iting temperature of C. and at a maximum voltage of' 45 volts with no load. The'minimum speed would be reached at a minimum temperature of minus 20 C., a minimum voltage of 28 volts and a full load. Accordingly, the field windings are so proportioned and the current values are so regulated that the speed variation 01' the motor alternator is maintained within permissible limits throughout the ranges of these extreme conditions. Figure 4 shows a set of curves designated I, II, III, IV, V and VI, showing the variation in current in the speed-regulating field winding 2| as the frequency varies and under the, various extreme conditions outlined. The normal speed of the motor alternator is 3600 R. P. M. so that the normal output voltage is at 60 cycles per second. During operation it is per missible that the speed and frequency vary within limits of plus and minus 3.3 per cent. Thus the operating range is between the approximate limits of 58 and 62 cycles per second.

During actual operation, these limits are automatically maintained with the maximum speed at 3720 R. P. M. and with the minimum speed at 3480 R. P. M. At this maximum speed, the ratio of the magneto motive force of coil 2| to the magneto motive force of the main shunt field winding I1 is of the order of 74 to 1000 ampere turns per pole. This ratio changes as the motor speed decreases and at the minimum speed of 3480 R. P. M., this same ratio is 300 to 750' ampere turns per pole. Thus, if field coil 2| were not used, the ampere turnsper pole at the minimum speed compared to the maximum speed would be of the order of 750 to 1000 or 75 per cent. By using winding 2|, the ampere turns per pole are reduced from 926 to 450, which is a reduction from 100 per cent to 48.5 per cent.

In Figures 6 and 7, the voltages and currents of Figure at 62 and 58 cycles per second, respectively, are represented vectorially. Within this range of frequencies, circuit A has an inductive reactance and circuit B has a capacitiv react ance. As shown in Figure 4, the current reaches a minimum value at approximately 64 cycles per second and at this point, the impedance oi circuit A is very high and in cfiect is pure resistance, whereas the impedance of circuit B is very low and is capacitive.

In the embodiment of Figures -8 to 13, the motor alternator is the same as in the embodiment of Figures 1 to 7 but the speed-regulating circuit supplies current to field coil 2| in the reverse direction. Thus, field coil 2| tends to assist the main field winding so that the motor speed is kept down by increasing the current in coil 2|, and the motor speed is kept up by decreasing the current in coil 2|. Accordingly, within the operating speed and frequency range 01' the apparatus, the current to field coil 2| changes at a rapid rate with the speed, increasing when the speed starts to increase and decreasing when the speed starts to decrease. The resonant control circuit of this embodiment is formed by circuits A1 and B1 in series across lines 28 and 36. Circuit A1 comprises condenser I12 connected at terminals III and I13 in parallel with inductance coil I66 which is positioned on a leg I66 of a double-sided iron core assembly I64. The other leg I63 oi the iron core assembly I64 carries an inductance coil I62 and a condenser I" has one side connected to one side of inductance coil I62 at terminal I61. The other side of condenser I70 is connected to the input terminal I51 of the rectifier unit I56, the other input terminal I53 of the rectifier unit being connected through lead I59 and terminal I69 to' inductance coil I62. Terminal I66 is connected to line 30 and terminal I1 l-is connected to line 28. i

The output terminals I55 and I5| oi rectifier unit I 56 are connected respectively through leads 52 and 54 to the auxiliary field winding 2| of motor I8. It should be noted that leads 52 and 54 are of reversed potential in Figure 8 with respect to their potentials in Figure 1, and this is due to the fact that in operation rectifier unit I56 is reversed relative to rectifier unit 56. Core assembly I64 is provided with air gap in the same manner as is core assembly 64 of Figure 1.

In this embodiment, condensers I10 and I12 are of i0 microfarads and 30 microfarads capacity, respectively, and inductance coils I52 and I68 are of .445 henry and .265 henry, respectively. The normal operating speed of the motor generator is 3600 R. P. M., with sixty cycle output voltage, and the permissible frequency variation is from 58 to 62 cycles. Circuit A1 is in parallel resonance at 56.7 cycles per second, and circuit 131 is in parallel resonance at cycles per second.

Figure 9 is a simplified showing of the circuit of Figure 8. Thus, circuit B1 is shown as having one branch formed by inductance coil I62 and the other branch formed by condenser H0 in series with rectifier unit I56 and its output circuit, and circuit A1 is shown as having branches formed by inductance coil I68 and condenser I12. Circuits A1 and B1 are parallel resonant circuits similar to the embodiment of Figures 1 to 7, and may 'be represented by the equivalent circuit of Figure 3.

Figure 10 is a curve showing the variation in the current supplied to coil 2| as the speed and the output frequency change. Assuming that the motor alternator is operating at 3600 R. P. M., if there is an increase in speed and frequency, this increase is accompanied by a sharp increase in the current to coil 2|. This increase in current materially strengthens the motor field and tends to hold the motor speed down. Converse- 1y, as the motor speed starts to fall, there is a sharp reduction in the current of field coil 2|, and an accompanying decrease in the strength of the motor field.

In Figure 11, the notations correspond to those of Figure 5, with the total impressed voltage represented by E1. and line current represented by In; the voltages across circuits A1 and B1 are represented by EA and E3, respectively, and the current through the rectifier unit is represented by the notation In. In Figures 12 and 13 the v0ltages and currents of Figure 11 are represented vectorialiy at 62 and 58 cycles per second, respectively. Within this range of frequencies, circuit A1 has a capacitive reactance. and circuit B1 has an inductive reactance.

Referring again to Figure 10, at substantially 57 cycles, the current through field coil 2| is threehundredths amperes, whereas at 64 cycles, it is nine-tenths amperes, and the change is substantially straight-line variation between these limits. The apparatus is carefully adjusted to respond to this change, and accordingly, field coil 2| has sufilcient turns to limit the variation in frequency due to all causes to plus or minus 3.3 per cent from the normal 3600 R. P. M., 60 cycle, speed. This is accomplished with current not exceeding six-tenths amperes. As an example, the slowest speed during operation of a standard shunt motor having no speed control means occurs when the voltage is 28 volts, the temperature of the shunt field winding coil is minus 20 C., and the motor is fully loaded; at this point there are 750 field ampere turns per pole. The fastest motor speed pf operation is when the voltage is 45 volts, the temperature of the shunt field coil is 125 C., and the equipment is carrying no load; at this point there are 1000 field ampere result, when the present device is not used, the speed variation under these circumstances would be from 3720 R. P. M. to 2900 R. P. M. When the present device is used, the total field ampere turns per pole remains at 1000. at the high speed of 3720 R. P. M., but the ampere turns per pole is reduced to 480'at3480 R. P. M. which is the lowes speed attained.

Under some circumstances, it may be desirable to combine the features of the tapped inductance coils of the embodiment of Figures 1 to '1 with the features of circuit 131 oi Figures 8 to 13. Accordingly, in Figure 14, an embodiment of this nature is shown. In this embodiment, the results attained are similar to the results of the other embodiments. The elements represented-in Figure 2 and corresponding to elements of the other figures have been given corresponding numerals in the 200 range. Hence, line 28 is connected through lead 216 to tap 214 of inductance coil 268 which is in parallel with condenser 212, and this comprises circuit A2. Circuit B2 includes condenser 210, inductance coil 262, and rectifier unit turns per pole. As a 256 with its output circuit, and circuits A2 and B2 are connected by lead 218. The results attained are similar to the results of the other embodiments, and by properly proportioning the values of the various parts of the equipment, the operation of the motor generator is held within permissible limits. -In this embodiment condensers 210 and 212 are of 7.5 microfarads and 15 microfarads respectively, and inductance coils 262 and 208 are of .595 henry and .530 henry respectively. Tap 280 is such that an effect is obtained of there being 13.4 per cent of the turns between tap 280 and terminal 261; likewise, tap 214 is such that an efiect is obtained of there being 29.3 per cent of the turns between tap 214 and terminal 211.

As many possible embodiments may be made of the mechanical features of the above invention,

and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth. or shown in the accompanying drawings is to be interpretedas illustrative and not in a limiting sense.

I claim:

1. In an electrical system of the class wherein a motor alternator receives power from a direct current source and supplies alternating current netic flux of the motor, and means to supply auxiliary field current to said auxiliary field winding comprising two parallel resonant circuits connected in series across the output terminals of the alternator, one of said resonant circuits including a rectifier unit having its output leads connected to deliver the auxiliary field current.

3. In an electrical system of the class wherein a motor alternator receives power from a direct current source and supplies alternating current power to a load and wherein the motor of said motor alternator is provided with the major portion of its field flux by a shunt field winding, the combination with said shunt field winding of an auxiliary field winding which carries current to thereby tend to reduce the total magnetic flux as the motor generator speed falls, and means to supply current to said auxiliary field winding comprising two parallel resonance circuits connected in series across the output lines of the alternator, each of said resonance circuits including an inductance coil having an unsaturated iron core-.and having a tap intermediate its ends.

4. In asystem in which an alternator supplies power of substantially constant frequency and voltage to a load and the alternator is driven by a. motor, the combination with said motor and said alternator of means to supply auxiliary field current to said motor comprising a series circuit connected across the output terminals of said alternator and including a rectifier having its output terminals connected to deliver auxiliary field current to the motor, said series circuit comprising a first circuit and a second circuit with said rectifier forming a part of said second circuit, said first circuit comprising an impedance means and said second circuit including a parallel resonance unit which is in resonance at a frequency substantially near but other than the normal operating range of frequencies of the alternator.

5. In a system in which an alternator supplies power of substantially constant frequency and voltage to a load and the alternator is driven by a motor,'the combination with said motor and said alternator of means to supply auxiliary field current to said motor comprising a series circuit connected across the output terminals of said alterpower to a load and wherein the motor of. said motor alternatoris provided with the major portion of its field flux by a. shunt field winding, the

combination with said shunt field winding of an auxiliary field windingwhich carries current to thereby tend to effect a change in the total magnetic fiux of the motor, and' means to supply auxiliary field current to said auxiliary field winding comprising two parallel resonant circuits connected in series across the output terminals of the alternator.

2. In an electrical system of the class wherein a motor alternator receives power from a direct current source and supplies alternating current power to a load and wherein the motor of said motor alternator provided with the major portion of its field flux by a shunt field winding, the combination with said shunt field winding of an auxiliary field winding which carries current to thereby tend to effect'a change in the total magnator and including a rectifier having its output terminals connected to deliver auxiliary field current to the moto said series circuit comprising a first circuit and a second circuit with said rectifier forming apart of said second circuit, said first circuit comprising a condenser unit and an inductance unit *Twhich are connected in parallel and are in resonance at a frequency which is substantially one of the limits of the range of operating frequencies, and said second circuit comprising an inductance unit and a condenser unit connected in parallel and said rectifier circuit having its input terminals connected across a portion of said inductance unit.

6. A system as claimed in claim 4, wherein said auxiliary field current tends to set up magnetic fiux which adds to the main magnetic fiux and wherein said first circuit is a resonant circuit and is in resonance at a frequency above the normal operating frequency and said second circuit is in resonance at a frequency below the normal operoperating frequency and said second circuit is in resonance at a frequency above the normal operating frequency with the result that said auxiliary current is increased as the motor speed increases.

8. A system as claimed in claim 4, wherein said first circuit comprises a condenser unit and an inductance unit which are connected in parallel and are in resonance at a frequency which is substantialiy the lower limit of the range of operating frequencies, and wherein said second circuit comprises an inductance unit connected in parallel with a condenser and the rectifier circuit, said rectifier circuit having its input terminals connected in series with said condenser with said second circuit in parallel resonance at a frequency which is substantially above the upper limit of the range of operating frequencies.

9. A system as claimed in claim 5, wherein said first circuit has a tap on its inductance unit which is connected to one of the output terminals of the alternator and one side of said first circuit is connected to a tap on the inductance unit of said second circuit, and wherein said first circuit is in resonance at a frequency which'is substantially the upper limit of the range of operating frequenof the alternator normal operating cies and said second circuit is in resonance at a frequency which is substantially below the lower limit of the range of operating frequencies.

10. In an electrical system in which an alternator supplies power of substantially constant frequency and voltage to a load and the alternator is driven by a direct current motor the speed of which varies with variations in field flux, the combination with said motor and said alternator of auxiliary means to supply auxiliary field current to the field winding assembly of the motor comprising a series circuit connected across the output terminals of said alternator and including a rectifier having its output terminals connected to deliver the auxiliary field current, said series circuit comprising a first circuit and a second circuit with of the said second circuit, said first circuit comprising an impedance means and said second circuit including a resonance unit which is in resonance at a frequency substantially near but other than the normal operating range of frequencies whereby a departure from said range of frequencies causes a rapid change in the auxiliary field current.

LABEEB B. HADDAD.

said rectifier forming a part 

